AL-26 IN IRON-METEORITES AND THE CONSTANCY OF COSMIC-RAY INTENSITY IN THE PAST

Cosmic-ray-produced 26Al in iron meteorites has been measured by low-level γγ-coincidence counting. The 26Al activities, in dpm/kg, are: Aroos 3.0 ± 1.0, Braunau 2.6 ± 0.5. Kayakent 4.6 ± 1.5, N'Goureyma 4.4 ± 1.1, Okahandja 3.6 ± 0.9, Treysa 4.0 ± 0.5. Exposure ages based on 26Al/21Ne are in agreement, within experimental error (±20%), with those based on 36Cl/36Ar and 39Ar/38Ar but the ages based on 40K/41K are higher by about 50%. The difference in exposure ages is probably caused by a real change of the cosmic ray intensity in the inner solar system. © 1979.